The aim is to understand how platelet adhesion and activation are affected by surface properties of polymers which have been chosen for their potential in biomedical applications, and to relate these responses to their effects on thrombogenicity. The activation of purified human platelets on polymer surfaces, which have been previously characterized by X-ray photoelectron spectroscopy, contact angle, and other techniques; will be studied by Scanning Electron Microscopy, High Voltage Electron Microscopy, and in the living state, by Video-enhanced Differential Interference Contrast Light Microscopy. Differences in cytoskeletal reorganization during shape-change, time and rate of shape-change, appearance and motility of platelet surface receptors, and granule secretion will be analyzed for each surface. Monoclonal antibodies and specific ligands conjugated to colloidal gold will be employed as probes to follow receptor motility by both light and electron microscopy. Differences in shape-change will then be analyzed using pharmacologic agents to modify activation, receptor expression, and cytoskeletal reorganization. These observations will then be related to polymer physicochemical properties. Additionally, three parameters of platelet function which affect thrombogenesis will be analyzed in vitro for the different polymers. These are; platelet dense granule secretion by photoluminescence ATP assay, immuno-gold bead studies of receptor expression, and the extent of activation inducible by platelet agonists. With an iterative process polymers with other surface properties will then be examined. Ultimately, the determination of polymer surface properties which are important in modulating platelet adherence and activation is desired. An understanding of how platelets respond to polymers having different surface properties can provide a basis for developing polymers with minimal adverse effects when placed in the circulation. Knowledge of the mechanisms by which platelets alter their responses to surfaces, as studied through pharmacologic means, could also lead to improved anticoagulant therapies when artificial materials are placed in the circulation. In addition, the observations of receptor appearance and motility, and granule secretion will lead to a better understanding of the platelets' role in modulating thrombosis and to improved in vitro assays for surface thrombogenicity.